A) Gastrin Releasing Peptide Receptor: Model System. Gastrin-Releasing Peptide is a 27 amino acid peptide derived from a proGRP precursor, of which there are least three types which differ in relation to alternative splicing at the 3' end of the precursor in a location not involving the GRP portion of the molecule. To focus on the nature of a receptor for GRP, GH3 cells, a cloned rat pituitary cell line demonstrated enhanced phosphoinositide turnover in response to binding of bombesin. This process was partially sensitive to pertussis toxin and could be elicited by as low as 0.15 uM bombesin. On examining SCLC cultures, preliminary experiments suggest a small but reproducible tumor in phosphoinositide turnover after addition of bombesin to a cell line known to have receptors. Crosslinking agents have been used to confirm specific binding of labelled GRP to GH3 and 3T3 cells, and will be used in further attempts to characterize and perhaps purify the GRP receptor. B. Guanine Nucleotide Regulatory Protein in Lung Cancer. Using type specific antibodies, identification of Gs, Gi and Go was accomplished in several small cell lung cancer cell lines. The physiologic relevance of these proteins as regulators of human induced second message system will be explored, via effects on cell growth, and interactions with other membrane molecules by cross linking agents will be explored. The significance of these studies is that definition of an autocrine role for gastrin-releasing peptide by others in the lab needs to be pursued with respect to how the growth activated pathway is mediated. Points where this pathway feeds into intermediary metabolism could allow design of rational therapeutic approaches.